The past several decades have seen considerable advancement in engineering materials through the development of improved composite materials. Composites allow designers to combine advantageous features of multiple component materials to arrive at a material that typically has one or more different properties than the component materials individually.
One area that has seen particularly rapid advancement is the area of reinforced plastics. For example, it is popular to improve properties of a plastic by incorporating an inorganic reinforcement phase, such as the employment of a fiber that is made of glass, carbon, metal or another inorganic material. In a number of instances, a form is provided that incorporates the inorganic reinforcement material, and is impregnated or otherwise intermixed with a thermoplastic or thermoset plastic matrix. One particular example that has seen increased popularity in recent years is a Glass Mat Thermoplastic (GMT) composite, which ordinarily employs a glass mat reinforcement phase that is impregnated with a thermoplastic such as polypropylene. The difference of material types between the glass and the thermoplastic matrix tends to complicate any reclamation or recycling efforts with these GMT materials.
In recent years, the plastics industry also has seen experimentation in the development of thermoplastic “fabrics” that employ a weave of one or more thermoplastic fibers, with or without a glass fiber as well. Typically, these materials are offered in a woven and consolidated form, namely, upon weaving the fibres, they are heated to melt at least a portion of their outer surface. Upon solidification, adjoining fibers are solidified together.
To date, efforts to provide a suitable thermoplastic reinforcement form that can readily be processed to form a resulting article, particularly an article that is shaped by molding or forming under elevated temperature, have been limited. It has been observed, for example, that the step of consolidation (wherein the fibers or other units of the reinforcement form are heated to fuse together), requires at least a first heat history, and the step of forming the resulting shaped article requires at least a second heat history. With each additional heat history, the opportunity for morphology change is increased, with the attendant loss of mechanical properties, such as impact strength.
A review of various polypropylene composite technologies is provided in the thesis of Cabrera, “Recyclable All-Polypropylene Composites: Concept, Properties and Manufacturing”, Technische Universiteit Eindhoven (2004)(ISBN 90-386-2676-2), incorporated by reference herein.
Accordingly, there is a need for improved composite systems that overcome one or more of the obstacles faced by existing materials.